This application claims the priority of German application, filed Mar. 11, 1997, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a method and apparatus for improving the quality of exhaust gas emissions from an internal combustion engine having an exhaust catalyst which is heated after the engine is started, and the power output of the generator is reduced during this warm-up phase of the exhaust catalyst until the exhaust catalyst has reached a specific minimum temperature. The attainment of the operating temperature can be detected, for example, by measuring the temperature or by also evaluating the time the heating system takes to turn on.
German Patent Document DE 39 39 068 C2 discloses a method of this kind, in which the catalyst heater is separated from the generator and is operated only by the battery during the warm-up phase of the catalyst. Since the heater is turned on for a relatively short period of time, the load on the battery will not be excessive. As a result, exhaust gas emissions improve, since the load on the engine is relieved by the reduction of the drain on the generator. Cleaning of the exhaust by the catalyst does not begin until the exhaust catalyst has reached its operating temperature. The specific minimum temperature is therefore this operating temperature, or one that is slightly lower. To achieve this result, it is also known to provide a plurality of generators of which only one is in operation during the warm-up phase of the exhaust catalyst.
German Patent Document DE 43 35 771 C1 also discloses a method in which a heater heats the exhaust catalyst during the warm-up phase of the exhaust catalyst because this heater is supplied with electrical energy. Since this heater (operated by electrical energy) is a comparatively heavy load upon the generator, the power output of the generator is increased in order to keep the load placed on the batteries by the heater within predefined limits. Further, the exhaust catalyst should reach its working temperature as quickly as possible. This is so that the exhaust catalyst can serve its purpose and improve the exhaust gas emissions of the internal combustion engine as early as possible during the operation of the internal combustion engine. To cover the power demanded by the heater the generator is regulated so that, in the warm-up phase of the exhaust catalyst, the power output of the generator is increased.
An object of the present invention is to improve the exhaust gas emissions of an internal combustion engine, while at the same time limiting the load on the battery system.
This and other objectives and advantages are achieved by the method according to the invention, in which during the warm-up phase the power output of the generator is adjusted by reducing the power output of the generator by an intervention into the latter such that it is greater than 0, while the power with respect to normal operation is reduced after the warm-up phase. The intervention can be made, for example, by electrically deactivating the generator.
In comparison to the procedure disclosed in German Patent Document DE 39 39 068 C2, where support for the battery by a residual power of a generator is provided by using a generator system which consists of several generators, during the warm-up phase of the present invention only one of the generators is in operation. This provides an advantage in the method according to the present invention in that only one generator is needed as a component, where the power of this one component is appropriately adjusted.
From German patent document DE 40 42 347 A1, it is known to reduce the power output of the generator until the internal combustion engine has reached its operating temperature. This measure is intended to serve as a method for avoiding rough operation of the internal combustion engine. Here, no mention is made of reducing exhaust gas emissions. Since the disclosure of DE 40 42 347 is directed to the operating temperature of the internal combustion engine and not the operating temperature of the exhaust gas catalyst, DE 40 42 347 is directed to a different purpose than the present disclosed invention.
Thus, in accordance with the objectives of the invention, the load on the internal combustion engine is reduced until this operating temperature is reached. By reducing the load on the internal combustion engine, the pollutant output of the internal combustion engine is reduced until the exhaust gas catalyst intervenes.
The heating capacity of the exhaust gas catalyst's heater is assisted, for example, by a battery which is recharged when the exhaust gas catalyst has reached its operating temperature. As a result of this method, at least under certain conditions of operation during sufficient periods of time in which the battery is charged, an improvement of the overall balance of the exhaust gas emissions is achieved. Excessive discharging of the battery is advantageously avoided because to a certain extent the generator is still supplying power.
In the method according to an embodiment of the invention, the generator's output is regulated such that it does not drop below certain on-board line voltage limits.
Thus a guarantee of the operation of other electrical devices is advantageously assured. This is especially significant in safety-related functions, such as for example, the airbag or an antilock brake system for the wheels of the vehicle.
Likewise, in order to reduce the total current demand up to the time that the exhaust gas catalyst reaches its operating temperature, it is also contemplated to reduce the number of engaged electrical devices according to their importance to the safe operation of the motor vehicle. Various methods are known for reducing the power consumption of electrical devices in a motor vehicle in which easing the battery load is of primary importance. The procedure used in these methods might also be applied at this point to the method described hereinabove.
Other objectives, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.